Seminar reports:
Spectra from Exoplanets and stars

Contents:

• Characterising the Atmospheres and Circumplanetary Environment of Exoplanetsby Ernst de Mooij
• Radial Velocities and Wavelength Shifts - Stellar Spectra and Exoplanet Detectionby Dainis Dravins
• Seminar scheduleSeminar schedule

How to cure a boring day:

Sometimes I can feel that I have very boring days, what to do? At the university where I live in Stockholm you can find a lot of interesting seminars during day time. I decided to make one day free each week to visit these seminars, the seminars I write about here are about astronomy. One thing that have made me very interested the last 30 years is about origin of our life, does the small building blocks (molecules) of life comes from outer space? Then it should be life on a lot of other planets, maybe primitive forms in our own solar system and other planets around other stars. About planets in outer space we first have to find those planets around other stars, Exoplanets. There are many techniques to use, one of them are about to study the Doppler shift in the spectra from the star that the Exoplanets orbit around.

Some useful links:

Exoplanets:

• https://en.wikipedia.org/ wiki/ Exoplanet (Exoplanet, Wikipedia)

Doppler effect:

• https://en.wikipedia.org/ wiki/ Doppler effect (Doppler effect, Wikipedia)

Characterising the Atmospheres and Circumplanetary Environment of Exoplanets:

By Dr Ernst de Mooij

My first visit to one of these seminars was one with Dr Ernst de Mooij from Dublin University.

You can read his abstract here:
"Since the discovery of the first planet outside our solar-system almost 25 years ago, the field of exoplanet research has made a lot of progress. Not only has the number of known exoplanets increased to over 3000, the atmospheres for a number of exoplanets have been detected. These atmospheric studies have mainly been made for transiting planets. For these planets is not only possible to study their atmosphere in emission / reflection during the secondary eclipse and through their phase-curve, but also in transmission during the transit. I will show that ground-based telescopes can be used to reach the high precision required to detect the atmospheric signatures, while long-term monitoring with space-based telescopes allows us to start and probe dynamics in the atmospheres of alien worlds. Finally, I will show how we can use high-resolution spectroscopy to search for rings around exoplanets."

This was a very interesting speech, when they detected the first Exoplanets in the 1990s they had a resolution of the radial speed of some meters in the Doppler shift. Now they have sub meters resolution. There are now so much details in the spectra Ernst tell that you can even see if the Exoplanets have rings as our own giant planet Saturn have.

Sorry about that this was a bit short, but didn't plan to write that much as I want now and didn't take that much notes.

More to read about Ernst de Mooij and his research:

• https://www.irishtimes.com/ topics/ topics-7. ... (Ernst de Mooij, The Irish Times)

Radial Velocities and Wavelength Shifts - Stellar Spectra and Exoplanet Detection:

By prof. Dainis Dravins

Next seminar was with prof. Dainis Dravins from Lunds University.

You can read his abstract here:
"Highest-precision radial velocities are needed both to find Earth-like exoplanets and to follow the expansion of the Universe. While the required instrumentation is becoming available, limitations are now set by the physics of spectral-line formation. Dynamical motions in stellar atmospheres cause spectral lines to become asymmetric and their wavelengths to “flicker”. 3-D hydrodynamic models reveal patterns of wavelength displacements across stellar disks and such models can now be tested also for stars other than the Sun, exploiting exoplanet transits. Differential spectroscopy between various transit phases provide spectra of small stellar surface segments temporarily hidden behind the planet. Ongoing exoplanet surveys are likely to find additional suitable host stars for spatially resolved stellar spectroscopy, identifying routes toward finding “true” Earth analogs."

When measuring Doppler effects of just a few 10 centimeters radial speed you get a lot of disturbances from the stellar atmosphere. If you knows its behavior, you can include its effect in the calculations and thereby penetrate deeper into the spectrum and get more details about the exoplanet.

Dainis tells about the history when Freundlich's attempt to verify the theory of relativity.

When doing high resolution Doppler measuring you have to know the gravitational redshift and its influence of the stellar spectra.

With models of our solar atmosphere you can simulate the stars spectra behaviors on local scale, it differs along the main sequence.

Dainis tells:
"A "Jupiter" covers about 10'000 solar-type granules"

When a Exoplanet pass in front of a star it blocks part of its spectra. With subtraction technique you could get a very high spatial resolution of the stars spectra. The spectra differs from the center to the edge. Part of it because you see the surface movements from different angles.

When the exoplanet pass in front of the star and if the planet has an atmosphere you get an absorption spectra from it.

When the exoplanet pass behind the star and then subtract the star spectra from the spectra just before the exoplanet disappear you get an reflection spectra from the exoplanet's surface.

You can read more about Dainis Dravins research here:

• https://portal.research.lu.se/ portal/ sv/ persons/ dainis dravins ... (Dainis Dravins, Lunds University)
• http://www.astro.lu.se/ ~dainis/ (Dainis Dravins, Lunds University)

These seminars was a good cure to my boring days. Do you have boring days too? Join me next time!

• https://www.nordita.org/ events/ seminars/ schedule/ (Theory seminar schedule, Nordita)

If you not live in Stockholm in Sweden as I do I'm sure that you can find something similar to visit at your place. Or you do as all other do, search the internet, TED Talks is good.

• https://www.ted.com/ (TED Talks)

No more boring days!